1. Field of the Invention
The present invention relates to a field emission light source device, more particularly, to a field emission light source device with improved light utilization efficiency.
2. Description of Related Art
A field emission lamp is developed to replace a fluorescent lamp owing to the advantages of the former, such as its simple structure, high brightness, power saving feature, and its ability to satisfy the requirements of flatness and large scale. Moreover, in addition to light source systems for decoration, lighting or indication, a field emission lamp can further be applied to the backlight modules of LCDs.
FIG. 1 is a schematic view for illustrating the work principle of a field emission light source device. A field emission light source device mainly includes a cathode electrode 12, an electron emissive layer 14, an anode electrode 15, a phosphor layer 16 and a gate electrode 19. Herein, the anode electrode 15 and the phosphor layer 16 are formed on the front substrate 17, while the cathode electrode 12, the electron emissive layer 14 and the gate electrode 19 are disposed on the base substrate 11. Accordingly, when a voltage is applied between the cathode electrode 12 and the gate electrode 19, an electric field is formed between the cathode electrode 12 and the gate electrode 19 and thus the tunnel effect occurs whereby electrons are released from the electron emissive layer 14. Then, a voltage applied on the anode electrode 15 would accelerate the impact of the released electrons to the phosphor layer 16, resulting in the emission of light from the phosphor layer 16. Moreover, the gate electrode 19 can be used to accurately control the emission of electrons and to increase the electron current density, and the gate electrode 19 and the cathode electrode 12 can be electrically separated from each other by the insulating layer 13.
In general, electrons released from the electron emissive layer 14 merely impact to the surface 161 of the phosphor layer 16, and thus the highest luminous efficiency would be found from the surface 161 of the phosphor layer 16. That is, most of light emitted from the phosphor layer 16 is limited within the device and thus cannot be transmitted outwards. In addition, since the output window of the conventional field emission light source device is located against the surface 161 of the phosphor layer 16, the light transmitted outward from the surface 161 of the phosphor layer 16 has to pass through the phosphor layer 16, the anode electrode 15, and the front substrate 17, which results in the reduction of light extraction efficiency. Thereby, the aforementioned conventional field emission light source device generally has the disadvantage of low luminous efficiency.